CHICAGO (AFP) – – Biologists have mapped how a deadly class of viruses including dengue, West Nile, yellow fever and encephalitis become infectious in a pair of studies published in the journal Science.

“This is possibly the most detailed understanding of how any virus matures,” said study author Michael Rossmann of Purdue University in Indiana.

Rossmann and his colleagues detailed critical structural changes that take place as the dengue virus moves from the inner to the outer portions of its host cell.

The findings pertain to all viruses in the family of flaviviruses which are carried by mosquitoes and ticks.

They found that a protein which coats the genome of the virus particle undergoes large changes in its structure so that it becomes capable of fusing with cell membranes.

This structural change, which occurs as the virus is being secreted from its host, allows the protein to infect other cells rather than attaching itself to its host.

“It’s like a bird being pushed out of the nest and suddenly being able to fly,” Rossmann said in a telephone interview.

This transformation occurs as the virus is exposed to progressively less acidic conditions which change the protein structure in its outer shell.

“This change in acidity was already known, but its impact on the maturation process was not known until these new findings,” Rossmann said.

This discovery could help researchers develop an antiviral treatment for dengue fever, which infects more than 50 million people and kills about 24,000 each year.

“There are a number of places where small drug compounds might interfere with the changes which we describe,” he told AFP.

A vaccine has not yet been developed for dengue fever because multiple exposures can actually increase the risk of developing the more deadly dengue dengue hemorrhagic fever.